A liquid crystal on silicon (LCOS) panel employs semiconductor technology to control liquid crystal to “project” color images. LCOS panels have become a new-type reflective projective panel and have various advantages when compared to transmission-type liquid crystal displays (LCDs) and digital light procession (DLP) panels. Such advantages include higher light utilization, higher contrast image, smaller size, higher aperture ratio and mature fabrication technology. They can easily achieve high resolution and satisfying color performance. These advantages promise LCOS panels a predominant status in the future application field of large scale displays.
U.S. Pat. No. 5,963,289 discloses a manufacturing method of LCOS panel. As shown in FIG. 1, an LCOS panel manufactured by using this method includes a silicon substrate 400 and a glass substrate 500. A bond pad 700 for connecting to a peripheral circuit is provided on the silicon substrate 400 and a transparent electrode 530 is provided on the glass substrate 500. The silicon substrate 400 and the glass substrate 500 are asymmetrically scribed, and thereby the bond pad 700 on the silicon substrate 400 and a part of the transparent electrode 530 on the glass substrate 500 are exposed. In this method, in order to form an electrical connection between the LCOS panel and the peripheral circuit, the silicon substrate 400 of the LCOS panel is fixed on a printed circuit board (PCB) which provides a voltage to the silicon substrate 400 and the transparent electrode 530. In a general case, the bond pad 700 of the silicon substrate 400 is connected to the PCB through a wire, while the transparent electrode 530 is connected to the PCB through a conductive adhesive. For this reason, the silicon substrate 400 is designed to have an extension portion on one side and the glass substrate 500 is designed to have an extension portion, or overhang, on the opposite side. Electrodes for connecting to the peripheral circuit are located on the extension portions, respectively. In this method, the extension portions of the silicon substrate 400 and the glass substrate 500 protrude in opposite directions. As these extension portions are only for connection but not for display, an LCOS panel with such a structure will have a relatively large size.
To meet daily increasing demands for miniaturization of electronic products, various attempts have been made to reduce the size of LCOS panels. JP2005274665 discloses another LCOS panel, as shown in FIG. 2 and FIG. 3, the LCOS panel includes a silicon substrate 140 and a glass substrate 130, which are bonded together using a sealing material 151. A transparent conductive layer 132 is provided on the glass substrate 130, and common electrodes 161 are provided at four corners of the silicon substrate 140. The common electrodes 161 are located outside the area where the sealing material 151 is applied. A common material 162 is used to connect the transparent conductive layer 132 to the common electrodes 161. Compared with the LCOS panel as disclosed in U.S. Pat. No. 5,963,289, this LCOS panel eliminates the extension portion of the glass substrate 130. The connections between the transparent conductive layer 132 and the common electrodes 161 are achieved by using the common material 162, and the common voltage for the transparent conductive layer 132 is generated by some other circuit arranged on the silicon substrate. Therefore, this LCOS panel has a smaller size.
In JP2005274665, in order to prevent short circuit caused by contact between the common electrodes 161 and liquid crystal, and to prevent the common material 162, which is generally a conductive adhesive, from contaminating the liquid crystal, the common electrodes 161 are arranged outside the area where the sealing material 151 is applied. However, in the manufacturing process of the LCOS panel, as the sealing material 151 and the conductive adhesive (namely, the common material 162) are coated before the bonding of the silicon substrate 140 and the glass substrate 130, at which time the sealing material 151 and the conductive adhesive are not cured yet, the conductive adhesive may easily pass through the sealing material 151 and contact with the liquid crystal during or after the process of bonding the silicon substrate 140 and the glass substrate 130. As a result, the liquid crystal will be contaminated and short circuit will occur between the common electrodes 161 and the liquid crystal.
In addition, as shown in FIG. 3, in the above manufacturing process, as the areas of the sealing material 151 and the common electrodes 161 are nearly overlapped, it is almost impossible to prevent the contact between the conductive adhesive and the sealing material even if the materials are coated on predetermined areas with a strictly controlled accuracy. Thus, even a minor discrepancy generated in the process will lead to the overlapping between the conductive adhesive and the sealing material, and hence the contamination to liquid crystal by the conductive adhesive.
Overall, although the manufacturing method of the prior art is capable of reducing the size of an LCOS panel, its yield is very low. Further, critical manufacturing requirements will limit its application in mass production.